Silica-containing nucleating agent compositions and methods for using such compositions in polyolefins

ABSTRACT

Diacetals of sorbitols and xylitols are employed in polyolefins as nucleating agents. Diacetals of sorbitols and xylitol nucleating agents may be provided in granular or powder form from hoppers or mixing equipment into polyolefins during the formation of polymeric compositions and polymeric articles. Flow of diacetals of sorbitols and xylitols is improved by the use of certain silicas, in certain defined weight percentages. Submicron size range silica compounds may provide excellent flow enhancement properties when blended and used with diacetals of sorbitols and xylitols powder compounds. A hydrophobic silica mixed with diacetals of sorbitols and xylitols compounds also may provide enhanced flow properties for such mixture, as compared to mixtures using hydrophilic silica. Loading ranges of silica may be important in improving the flow of diacetals of sorbitols and xylitols compounds.

BACKGROUND OF THE INVENTION

Sorbitol acetals are employed in polyolefins as nucleating agents.Nucleating agents provide improved properties to polymers, includingspeeded polymer crystallization and reduced haze. One nucleating agentin widespread use is 1,3-2,4 di(benzylidene) sorbitol (known as “DBS”),which is sold by Milliken & Company as Millad® 3905 brand nucleatingagent. Other sorbitol acetal compounds used as nucleating agentsinclude: (1) bis(3,4-dimethylbenzylidene) sorbitol (sold by Milliken &Company as Millad® 3988 brand nucleating agent, also known as “DMDBS”);and (2) bis(p-methylbenzylidene) sorbitol, sold by Milliken & Company asMillad® 3940 brand nucleating agent (“MDBS”).

In polymer manufacturing and operations, sorbitol acetals may beprovided as an additive powder from a hopper into polyolefin processingequipment for mixing with polymer. Commercial DMDBS in powder form isshown in FIG. 1, and DMDBS crystal 9 is seen in the upper right portionof the FIG. 1.

Sorbitol acetals sometimes do not flow readily or easily from suchhoppers, which is a continuing challenge for operators of polymeradditive equipment. Sorbitol acetals are inherently cohesive andcompressible, which contributes to operational flow problems. Flowproblems may manifest themselves as bridging and plugging, whichsometimes results in reduced flow, or no flow at all. This is anoperational problem for polymer mixing operations.

There are at least two common industry approaches to alleviate flowproblems. The first approach employs neat sorbitol acetal powder withspecially designed equipment and procedures for increasing flow of thesorbitol acetal. The drawbacks of this approach include: (1) it can beexpensive to design special equipment; and (2) it may not be feasible orpractical to change procedures for sorbitol acetal addition in aproduction plant.

A second approach is to use a pre-blend which contains a chosen diacetalof sorbitol as one component and other additives at certain ratios. Thepre-blends are normally provided in the form of agglomerated pellets orgranules to improve flow properties. The literature that discloses thisapproach includes: U.S. Pat. No. 6,673,856 (Mentink), U.S. Pat. No.6,245,843 (Kobayashi, et al.), and Korean Published Patent ApplicationNo. 2003-0049512 (“Kwun”). Operational flexibility may be sacrificed dueto the fixed ratio among different additives. Pre-blends of this typemay have negative effects on the optical performance of the resultingclarified polymer parts, such as undesirable white specks or flecks infinished polymeric parts of polyolefins having pre-blended sorbitoldiacetals.

Kwun describes a method of solving flow and injection problemsassociated with sorbitol acetal nucleating agents using organiclubricants. Kwun suggests coating the sorbitol acetal containingcompound with an organic material (i.e. “lubricating component”). Kwunspecifically suggests employing organic lubricants such as R—COOH acids,wherein R comprises C₅-C₂₂ carbon chains. “Metal soap” type organiccoatings are recommended, as the most effective coatings for thisapplication. In one of the examples shown in the patent, a hydrophilicSiO₂ grade in micron size range was used in combination with an organiclubricating agent.

What is needed in the industry is a manner of improving the flowproperties of particulate sorbitol acetals without the use ofundesirable pre-blends, solvents, organic lubricants, and the like. Amethod and composition that can be applied without the addition ofcumbersome and costly mechanical equipment would be desirable. Acomposition or method of deploying into polymers particulate sorbitolacetal compounds in a manner to result in smooth and uninterrupted flowfrom hoppers would be highly desirable. A manner of achieving highquality, low haze, polymeric parts that are substantially free ofblemishes or undesirable specks would be highly desirable. The inventionrelates to improved flow of sorbitol acetal compounds, and is furtherdescribed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 2-9 below illustrate various aspects of the invention, while FIG.1 shows commercially known product.

FIG. 1 is a photomicrograph showing crystals of commercially known DMDBSclarifier (Millad 3988 brand clarifying agent) of a DMDBS crystal size(length) of about 3-9 μm, such as DMDBS crystal particle 9;

FIG. 2 shows DMDBS combined with micron size range silica, in which thesilica forms aggregates 16 that often are significantly larger than theDMDBS crystal particles 14;

FIG. 3 depicts a photomicrograph of one embodiment of the invention of aDMDBS with submicron size silica, in which the submicron size silicaparticles are significantly smaller than the DMDBS particle 18, andtherefore provide advantageous properties and serve as a flow aid to theblended DMDBS/silica additive composition;

FIG. 4 is a photomicrograph showing a DMDBS particle 18 of FIG. 3 whichcompares schematically the size and configuration of DMDBS particle 18to clusters of submicron size silica particles 22, in which submicronsize silica particles agglomerate to form clusters 20 a-c, as shown inthe FIG. 4;

FIG. 5 is a graph showing cohesive strength values for Examples 1-1through 1-5, a loading level comparison for micron size range silica,including a comparative DMDBS without silica, as further describedherein;

FIG. 6 is a graph showing cohesive strength values for Examples 2-1 to2-2; a comparison of hydrophobic to hydrophilic silica for micron sizerange silica, and as further described herein;

FIG. 7 is a graph showing cohesive strength values for Examples 2-1,2-2, 3-1 and 3-2, comparing submicron size, micron size, hydrophobic,and hydrophilic silica, as further described herein; and

FIG. 8 is a graph showing cohesive strength values for Examples 4-1through 4-5 as further described herein; and

FIG. 9 is a graph showing cohesive strength values for Examples 5-1 and5-2, which includes data on the efficacy of the invention as applied toMDBS (bis(p-methylbenzylidene) sorbitol).

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made to the embodiments of the invention, one ormore examples of which are set forth below. Each example is provided byway of explanation of the invention, and not as a limitation of theinvention.

It has been discovered that submicron size range silica compounds havinga reduced particle size may provide excellent flow enhancementproperties when blended and used with sorbitol acetal powder compounds.

Further, it has been discovered that in many instances a hydrophobicsilica mixed with sorbitol acetal compounds provides enhanced flowproperties for such mixture, as compared to mixtures using hydrophilicsilica (i.e. SiO₂). In general, and especially for micron size ranges,hydrophobic silica improves sorbitol acetal flow more than hydrophilicsilica.

It has been discovered as well that in some instances micron size silicaunexpectedly improves the flow properties of sorbitol acetal powder whenthe silica dosage as a percent of the overall additive composition ishigher than about 10 wt %. This is desirable, and unexpected, in partbecause some silica manufacturers recommend using less than about two(2) weight percent silica for the purpose of assisting in powder flow.See for example an internet address for a manufacturer:www.gracedavison.com/Products/Pharmpc2.htm, which recommends using about0.25% to about 1.0% of a hydrophilic silica, Syloid 224 FP®. Thediscovery in the course of the invention of this application thatsubstantial benefits may occur above ten (10) weight percent silica(which is more than five times greater than some of the industryrecommendations) is significant and unexpected.

In the practice of the invention, silica is capable of providing flowenhancement benefits in most instances without using organic lubricatingmaterials. Submicron sized silica desirably provides an opticalreflective index relatively close to that of polyolefins, and this hasbeen found to be very desirable in providing suitable haze values forfinished polymeric articles. Thus, use of submicron sized silica insorbitol acetal compounds minimizes the amount of undesirable adverseeffects upon the optical performance (i.e. haze levels) when applied ina polymer or polymeric article of manufacture.

Some types of silica significantly improve the flow properties ofsorbitol acetal compounds under appropriate conditions. The appropriateconditions may include one or more of the following: (1) sufficientloading (higher than conventional dosage of silica as a flow aid), and(2) chemical nature of the silica surface (hydrophobic silica usually isbetter than hydrophilic silica), and (3) an appropriate particle sizerange (submicron particle size silica). One or more of these factors maybe employed for improved flow.

The invention provides different additive compositions comprising asorbitol acetal compound and a silica having at least one of thefollowing properties:

The silica may be hydrophobic, as defined further below (property A).

The silica may be a submicron-sized silica component, as defined furtherbelow (property B).

The silica may be a silica component, wherein said silica componentcontains a silica fraction providing at least 1% by weight of saidadditive composition of silica particles, said 1% silica fraction havingparticles with an actual particle size of less than 1 μm (property C).

The silica may be a silica component, wherein said silica component hasan Mv value of less than about 20 μm and a D90 value of less than about50 μm, and wherein the weight percentage of said silica in the additivecomposition is equal or greater than about 10% (property D).

The silica may have only one of these properties or properties A and B;A and C; A and D; A, B and C; A, B and D; B and C; B, C, and D; B and D;C and D; or A, B, C and D in combination. Moreover, each of therespective additive compositions may be substantially free of organiclubricating agents.

Submicron Sized Silica Component.

An additive composition may be provided in another aspect of theinvention comprising a sorbitol acetal compound and a silica component,said silica component having a volume mean diameter (Mv) value of lessthan about 0.6 μm and a D90 value of less than about 1 μm.

“D90 value” means that the silica fraction of the additive compositionin this particular embodiment of the invention is such that ninety (90)% (vol. %) of the actual silica particles are less than about 1 μm indiameter. In another embodiments of the invention, a Mv value of lessthan about 0.4 μm and a D90 value of less than about 0.6 μm is provided.In a further embodiment, the Mv value is in the range of 0.1 to 0.3 μmand the D90 value is in the range of 0.3 to 0.5 μm. In otherembodiments, the weight percentage of the silica in the additivecomposition is from about 0.5% to about 30%, or from about 0.5% to about10%, or alternatively from about 1% to about 5%. A polymeric orcopolymeric article of manufacture comprising such compositions also maybe realized in the practice of the invention.

Threshold Minimum Amount of Silica in the Submicron Size Range.

In yet another aspect of the invention, a blend of a sorbitol acetalcompound and silica is disclosed. The silica in this particularembodiment may have several fractions, based upon particle size.However, at least one fraction of the silica provides greater than 1% byweight of the total additive composition and also exhibits an actualparticle size (Mv) of less than 1 μm. That is, it has been found that ifat least 1% by weight of the total additive composition (i.e.DBS/silica) comprises silica having a size of less than 1 μm, the blendprovides unexpectedly superior flow properties. Furthermore, in someembodiments of the invention, such an additive composition also mayprovide a D10 value of less than about 0.5 μm; meaning that 10% of thesilica particles are less than about 0.5 μm in diameter. This silica maybe hydrophobic, in one embodiment. The weight percentage of silica inthe additive composition further may be between about 0.5% and 30%, oralternatively between 0.5% and 10%. A polymeric article made using suchadditive composition is also desirable.

Relatively Higher Silica Loadings

In yet another embodiment of the invention, an additive composition isprovided in which the composition comprises a sorbitol acetal compoundand a silica component, in which the silica component has a size rangeMv value of less than about 20 μm and a D90 value of less than about 50μm; further wherein the weight percentage of the silica in the overalltotal additive composition is equal to or greater than about 10%. Thesilica component further may provide a Mv value of less than about 10μm, and a D90 value of less than about 25 μm, in one embodiment of theinvention. The weight percentage of silica in the additive compositionmay be between about 10% and 30% in yet another embodiment. The silicaalso may be hydrophobic, as one option, and polymeric articles may bemanufactured using such a composition.

In one embodiment, the invention provides a sorbitol acetal/silicaadditive composition that is substantially free of organic lubricatingagents, such as metal soaps of stearic acid and the like. That is, it ispossible to achieve unexpected and superior flow enhancement in sorbitolacetal compositions, in most instances, without the use of organiclubricants and/or metal soaps, or pre-blends.

In the practice of the invention, a method of employing any of thecompositions disclosed herein in the manufacture of a polyolefin,polymer, or copolymer is also contemplated. Shaped articles, moldedarticles, and the like may be made using such additive compositions.

Powder Flowability

One definition of powder flowability is the ability of a powder to flow.Powder flowability is usually described by several measurable flowproperties, including cohesive strength, internal friction, wallfriction, shear strength, tensile strength, bulk density, andpermeability. Cohesive strength is one of the most important andparameters employed to describe the powder flowability. Powders withpoor flow properties may develop certain flow problems, such as“bridging”, “rat-holing”, and “flooding”, in hopper feeding equipment.

Silica

Silica is naturally occurring silicon dioxide (SiO₂) in variouscrystalline and amorphous forms. Silica also may be chemicallysynthesized. Based on the different processes employed to synthesizesilica, several types of silica are commercially available, and may beemployed, depending upon the particular embodiment to be achieved:

(1) fumed silica, which is manufactured in a gas phase pyrogenic processby reacting silicon tetrachloride in an oxy-hydrogen flame above 1000°C. to offer exceptional purity;

(2) precipitated silica, which is produced in a wet process byacidification of sodium silicate solution under conditions that usuallydo not lead to a gel; and

(3) silica gel, which is produced by acidification of sodium silicatesolution under conditions to lead to gel formation and to provide aporous structure after drying.

The average primary particle size of fumed silica ranges from about 5 nmto about 50 nm, and the primary fumed silica particles form tightlyfused structure aggregates in the size range of 100 nm to 1 μm. On theother hand, mean particle size of precipitated silica ranges from 4 μmto about 15 μm, whereas that of silica gel, including the special formnamed called “aerogel,” can be about 4 μm and above.

Hydrophilic and Hydrophobic Silicas

Based upon the chemical nature after surface treatment, silica isdistinguished into two types in the industry: hydrophilic andhydrophobic, regardless of the silica particle size. Hydrophilic silicagenerally refers to the type without surface treatment after chemicalsynthesis and exhibits an affinity for water due to the presence of thesurface silanol groups. Hydrophilic silica may be wetted with water.Without surface treatment, synthetic amorphous silica is naturallyhydrophilic. Silica sold in the industry is typically identified clearlyby the manufacturer whether it is hydrophilic or hydrophobic silica.

Hydrophobic materials are water repellant. In general, hydrophobicmaterials do not absorb significant quantities of water (i.e. less thanabout 1.5%) and do not wet readily with water. A simple wetting testwith water is commonly used to determine if a sample is hydrophobic.Hydrophobic silica is chemically modified, and it may be determined byFTIR analysis.

Commercial grades of hydrophilic silica include Aerosil® and Sipernat®product lines from Degussa AG and Cab-o-sil® product line from Cabot.Hydrophobic silica refers to the type of silica whose surface ischemically modified by reacting the surface silanol groups with varioussilanes, silazanes, and siloxanes. Hydrophobic silica usually cannot bewetted with water. Commercial grades of hydrophobic silica includeAerosil® product line “R” series and Sipernat® product line “D” seriesfrom Degussa AG and Cab-o-sil® product line “TG” series and Nanogel®product line from Cabot.

In one aspect of the invention, the additive composition comprises asorbitol acetal compound and a hydrophobic silica. The loading of silicain such an additive composition may in some instances be in the range offrom about 0.5% to about 30%, or from about 0.5% to about 10%, andsometimes from about 1% to about 5%. A polymeric or copolymeric articlemay be manufactured using the additive composition.

The differentiation between hydrophilic silica and hydrophobic silicacan be effectively achieved by measuring different parameters such asmoisture vapor adsorption isotherm, contact angle, wettability, carboncontent, or infrared spectroscopy, to name a few.

Silica Geometry

Synthetic amorphous silica typically exists as a finely divided whitepowder. This powder consists of individual particles with irregularshapes and dimensions. In the dry state silica powders are found to beloose agglomerates of particles. Wetting the powder with a wettingagent, and applying dispersion energy, facilitates the microscopicevaluation of the de-agglomerated silica particles. These particles varyin size. Statistical methods must be employed to quantitatively describethe population.

Further examination of the silica powder using electron microscopyreveals that the particles are comprised of primary particles that arefused or tightly bound. The primary synthetic amorphous silica particletends to be spherical in shape and varies in size from about 5 to 500 nmdepending upon the manufacturing process used to prepare the powder.Clusters of these primary particles form the individual particles oraggregates. Thus the silica powder consists of loose agglomerates ofaggregates of primary particles. Weak electrostatic charges as well asmechanical forces hold the agglomerate together. For the purpose ofanalysis it is useful to disperse the powder in a liquid by stirring andapplying ultrasonic energy. This will produce a liquid dispersion thatis stable in size and suitable for analysis.

Various types of silica can be employed in this invention. The examplesand tables herein list several types of silica that can be used in thepractice of this invention. The practice and scope of the invention,however, is not limited to only those types recited herein.

Table 1 herein lists the silica grades that have been employed in theexamples of the invention and their particle size parameters. Forpurposes of this specification and claims made herein, measurements ofsubmicron particles are measured by dynamic light scattering, andmeasurements of micron-size particles (greater than about 1 um) aremeasured by laser diffraction, as indicated in Table 1. Aerosil® 300,Aerosil® R812, Aerosil® 150, and Aerosil® R972 are fumed silica fromDegussa AG. HDK H15 is a fumed hydrophobic silica from Wacker-ChemieGmbH. Sipernat® D13 and Sipernat® 22LS are precipitated silica fromDegussa AG. Syloid® 244 is a hydrophilic silica gel from Grace Davison.However, these silica grades are merely examples of the silica that canbe employed, and the invention is not limited to any particularmanufacturer or type, or grade of silica.

Particle Size Analysis

Optical microscopy is a fundamental technique for particle sizeanalysis. If a single particle is viewed at 500×, it is possible toestimate the diameter down to about 0.8 μm by comparison to a calibratedgrid. Observations may also be made about the shape of the particles andwhether they are transparent, absorbent, or reflective. Thesepreliminary observations are useful for the selection of an instrumentto accurately measure the entire population of particles in a powdersample.

Ultrasonic wet sieving involves the use of electroformed precisionsieves with openings as small as 5 μm. Typically, a 1-gram sample of thepowder is wetted with approximately 1 liter of dispersant fluid and thesuspension is filtered slowly through the vibrating sieve. Over-sizedparticles, which are too large to pass through the sieve, are dried andweighed so that a percentage value for the over-sized population may becalculated. Ultrasonic wet sieving is a technique to measure coarse endof a fine particle distribution, but like optical microscopy, it is nota practical method to measure the entire distribution so that an averageor mean particle size may be known. However, both microscopy and sievingare useful preliminary methods to determine the size range of a powdersample so an appropriate method can be selected.

Laser Diffraction

Laser diffraction is a common technique used to measure the sizedistribution of a powder. A sample is dispersed in a liquid and passedthrough a clear cell where it is illuminated by a laser. The scatteringpattern from the laser is detected by a light sensitive photodiodearray. The scatter pattern is related to the size distribution of theparticles exposed to the laser beam in that small particles scattermonochromatic light at large angles and large particles scatter at smallangles. This phenomenon is referred to as Fraunhofer diffraction and isthe theoretical basis for commercial laser diffraction instruments.

The detection range for laser diffraction instruments is as wide as 1 to2000 μm. Some instruments also use Mie theory to compensate for errorswith small particles to extend the lower detection range from 1 to 0.1μm. Laser diffraction instruments measure a volume based particle sizedistribution. For irregular shaped particles the diameters reported areequivalent spherical diameters.

Data from a laser diffraction instrument is often presented as ahistogram and the following statistical parameters are calculated todescribe the size distribution of the powder.

Volume Mean Diameter (Mv)—Volume weighted arithmetic average particlediameter (also known as the volume moment diameter or the D (4, 3).

Tenth Percentile (D10)—Particle diameter corresponding to 10% of thecumulative volume based distribution.

Fiftieth Percentile (D50)—Particle diameter corresponding to 50% of thecumulative volume based distribution.

Ninetieth Percentile (D90)—Particle diameter corresponding to 90% of thecumulative volume based distribution.

Dynamic Light Scattering

Dynamic light scattering is another popular method used to measure thesize distribution of fine particles. The technique uses a diode laser toilluminate particles in a suspension to develop optical frequency shiftinformation to measure particles that range in size from 0.001 to 6 μm.Particles in suspension are in constant random motion (Brownian motion)as a result of interactions and collisions with molecules of thesuspending fluid. In the Stokes-Einstein theory of Brownian motion,particle motion is determined by the suspending fluid viscosity. From ameasurement of the particle motion in a fluid of known temperature andviscosity, the particle size can be determined. Dynamic light scatteringuses optical methods to measure particle motion. Small particles have ahigh velocity and cause a large frequency shift whereas large particlesmove more slowly and cause small frequency shifts in the illuminatinglight source. Random particle motion, measured over time, may beilluminated by a laser and used to form a distribution of opticalfrequency shifts that can be used to calculate the size distribution ofthe powder.

The size distribution measured with dynamic light scattering is volumebased. It is common to use statistical values such as the mean (Mv),tenth percentile (D10), fiftieth percentile (D50), and ninetiethpercentile (D90) to describe the particle size distribution. Dynamiclight scattering is superior to laser diffraction for the measurement ofpowders with a size range predominately below 1 μm. Laser diffraction isa preferred method to analyze powders that contain particles greaterthan about 6 μm in size.

Analytical Methods

Both laser diffraction and dynamic light scattering techniques requirethat the powder be de-agglomerated and dispersed in a fluid. Throughexperimentation it has been determined that isopropyl alcohol (IPA) is asuitable wetting agent for both hydrophilic and hydrophobic syntheticamorphous silica. The powder is first wetted with IPA by stirring andthen is dispersed with ultrasonic energy. Physical properties for IPAand silica are listed below.

-   -   IPA Refractive Index—1.38    -   IPA Viscosity @ 15 C—2.86 cp    -   IPA Viscosity @ 30 C—1.77 cp    -   Silica Refractive Index—1.46    -   Silica Particle Shape—Non-spherical    -   Silica Particle Opacity—Transparent

More specifically, 0.75 to 1 gram of powder is added to 30 ml offiltered IPA in a 50 ml-glass beaker. The suspension is stirred with aspatula until the silica powder is wetted by the IPA. The beaker issonicated using a ⅜″ diameter, 750-watt ultrasonic probe for 3 minutesat a 5% power setting. Optical microscopy and ultrasonic wet sieving areused to evaluate the quality of dispersion and estimate the size rangeof the particles in the population for each sample of silica powder.

Dynamic light scattering is a suitable method to measure submicronsilica powders herein. The Nanotrac 150 manufactured by Microtrac, Inc.is a commercially available dynamic light scattering device with adetection range of 0.0008 to 6.5 μm. A sample of the silica dispersed inIPA is added to the Nanotrac 150 sample cell and a measurement is madein duplicate over a 200 second time interval. The particle sizedistribution is calculated with a computer using Microtrac Flex softwareversion 10.3.0.

Laser diffraction is used herein for measurements provided in thisspecification and claims which are above about 1 um, and laserdiffraction is generally useful for a detection range of about 0.1 to2000 μm. Silica powders with a significant fraction of the sizepopulation greater than 6 μm are beyond the upper detection range ofdynamic light scattering whereas they can readily be analyzed by laserdiffraction. The Microtrac S3500 is a commercially available laserdiffraction instrument manufactured by Microtrac, Inc. The instrumentuses a three-laser system and an external sample circulation system togenerate a volume based size distribution. Silica powders are analyzedby first dispersing them in IPA using an ultrasonic probe thentransferring a representative sample of the dispersion to the samplecirculation system which contains IPA. The dilute suspension circulatesthrough a sample cell where the particles are illuminated by laserlight. The diffraction pattern over three 30-second time intervals isrecorded and the size distribution is calculated by a computer usingMicrotrac Flex software version 10.3.0.

In addition to the normal volume based statistical parameters, a numberbased mean particle size (Mn) is calculated and recorded. The Mn gives agreater weight to the smaller particles in the distribution and is shownwith the volume based mean particle size for comparative purposes. TABLE1 Samples of Silica Employed in the Invention Analytical Sample IDSilica Type Method D10 μm D50 μm D90 μm Mv μm Mn μm Aerosil FumedDynamic 0.082 0.183 0.346 0.21 0.15 300 Hydrophilic Light ScatteringAerosil Fumed Dynamic 0.05 0.17 0.46 0.24 0.13 R812 Hydrophobic LightScattering Aerosil Fumed Dynamic 0.11 0.22 0.43 0.26 0.20 150Hydrophilic Light Scattering Aerosil Fumed Dynamic 0.13 0.25 0.49 0.290.22 R972 Hydrophobic Light Scattering HDK Fumed Dynamic 0.13 0.24 0.460.30 0.22 H15 Hydrophobic Light Scattering Sipernat Precipitated Laser5.0 10.8 22.4 12.7 9.0 D13 Hydrophobic Diffraction Syloid Gel Laser 5.49.9 17.1 10.8 8.8 244 Hydrophilic Diffraction Sipernat PrecipitatedLaser 3.6 8.4 21.5 13.8 6.8 22LS Hydrophilic DiffractionDiacetals of Sorbitol (Sorbitol Acetal Compounds)

Clarifying agents of interest for use with the particular silicadescribed herein include diacetals of sorbitols and xylitols having thegeneral formula

where R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀ are the same or differentand each represents a hydrogen atom, an alkyl group having 1 to 8 carbonatoms, an alkoxy group having 1 to 4 carbon atoms, an alkoxycarbonylgroup having 1 to 4 carbons, a halogen atom, an hydroxy group, analkylthio group having 1 to 6 atoms, an alkylsulfoxy group having 1 to 6carbon atoms, or a 4 or 5 membered alkyl group forming a carbocyclicring with adjacent carbon atoms of the unsaturated parent ring; nrepresents 0 or 1. Of particular interest are clarifying agents where nis 1 and R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀ are selected from C₁₋₄alkyl, chlorine, bromine, thioether and a 4-membered alkyl group forminga carbocyclic ring with adjacent carbon atoms of the unsaturated parentring. Examples of specific clarifiers include: dibenzylidene sorbitol,bis(p-methylbenzylidene) sorbitol, bis(o-methylbenzylidene) sorbitol,bis(p-ethylbenzylidene) sorbitol, bis(3,4-dimethylbenzylidene) sorbitol,bis(3,4-diethylbenzylidene) sorbitol,bis(5′,6′,7′,8′-tetrahydro-2-naphthylidene) sorbitol,bis(trimethylbenzylidene) xylitol, and bis(trimethylbenzylidene)sorbitol.

Also within the scope of the present invention are compounds made with amixture of aldehydes, including substituted and unsubstitutedbenzaldehydes, and the like.

The clarifying agents of interest also include diacetals of sorbitolsand xylitols having a non-hydrogen substituted on the first carbon (i.e.C₁) of the sorbitol chain, as shown in the general formula (11):

where R may be selected from the group consisting of: alkenyls, alkyls,alkoxys, hydroxyl alkyls, and haloalkyls, and derivatives thereof; R₁,R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀ are the same or different and eachrepresents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms,an alkoxy group having 1 to 4 carbon atoms, an alkoxycarbonyl grouphaving 1 to 4 carbons, a halogen atom, an hydroxy group, an alkylthiogroup having 1 to 6 atoms, an alkylsulfoxy group having 1 to 6 carbonatoms, or a 4 or 5 membered alkyl group forming a carbocyclic ring withadjacent carbon atoms of the unsaturated parent ring; and n represents 0or 1.

Of particular interest are clarifiers where R is methyl, ethyl, propyl,butyl, allyl, or crotyl, R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀ areselected from C₁₋₄ alkyl, chlorine, bromine, thioether and a 4-memberedalkyl group forming a carbocyclic ring with adjacent carbon atoms of theunsaturated parent ring.

Examples of specific clarifiers that may be mixed with silica andemployed in the practice of the invention include:1,3:2,4-bis(4-ethylbenzylidene)-1-allyl-sorbitol,1,3:2,4-bis(3′-methyl-4′-fluoro-benzylidene)-1-propyl-sorbitol,1,3:2,4-bis(5′,6′,7′,8′-tetrahydro-2-naphthaldehydebenzylidene)-1-allyl-xylitol,bis-1,3:2-4-(3′,4′-dimethylbenzylidene)-1-methyl-sorbitol, and1,3:2,4-bis(3′,4′-dimethylbenzylidene)-1-propyl-xylitol.

One sorbitol acetal clarifier that may be employed is Millad® 3988,which is manufactured and distributed by Milliken & Company ofSpartanburg, S.C. Its chemical identity is1,3:2,4-bis(3,4-dimethylbenzylidene sorbitol), and it is known as“DMDBS”. Millad® 3988 used in this specification is the commercialgrade, which is manufactured with a step of milling through an air-jetmill to afford the ultra fine particle size of particles (d97 of 30microns or less, and a mean particle size of 15 microns or less) that isuseful to achieve its full clarifying power.

One surprising finding in the invention is that there is a “fit” orsynergy between silica particle and the primary sorbitol acetalparticle, which is unexpected.

A second example, Millad® 3940, is manufactured and distributed byMilliken & Company of Spartanburg, S.C. Its chemical identity is1,3:2,4-bis(4-methylbenzylidene sorbitol), and it is sometimes known asMDBS. Millad® 3940 used in this specification is the commercial grade.The practice and scope of this invention, however, is not limited tothese two examples.

Thermoplastic Polymers and Copolymers

Polyolefins are widely used in article applications including housewarecontainers, bottles, cups, syringes, pipes, films, and the like throughvarious processing methods such as injection molding, extrusion blowmolding, thermoforming, and casting. In many applications, transparencyor clarity of such plastic parts is desired. Clarifiers such as Millad®3988 are used in these applications to provide to the plastic articlesdesired optical properties. Typical polymers using clarifying ornucleating agents are polypropylene homopolymer (HPP), polypropylenerandom copolymer (RCP), polypropylene impact copolymer (ICP). Millad®3988 also clarifies some polyethylene resins, like linear low densitypolyethylene (LLDPE), low density polyethylene (LDPE), and high densitypolyethylene (HDPE).

The polyolefin employed in the examples herein is Profax SA849, which isa spheripol polypropylene random copolymer with approximate 12 MFR (g/10min). The practice and scope of the invention, however, is not limitedto SA849 RCP, or even to any particular polymer or polyolefin. Manyother polyolefin grades could be successfully employed in the practiceof the invention.

Flowability Measurement

To quantify the effect of silica in reducing the cohesive strength ofDMDBS, and thereby improving the powder's flowability, Jenike-Schulzering shear tests were performed to determine the cohesive strength ofthe following examples according to ASTM standard D6773-02. Data shownin the tables and Figures related to the examples indicate therelationship between the cohesive strength of the powders as a functionof consolidating pressure. Typically, as a powder is compressed, itscohesive strength increases. Flowability improvement on a given powderformulation is demonstrated by a lower line in the graph compared withthe control comparative (see FIGS. 5-9).

COMPARATIVE EXAMPLE

100% DMDBS is used as the comparative example for all sets of examples.Its cohesive strength data is listed in following tables. This exampleis made by stirring DMDBS (50 g) at ambient temperature for 20 secondsusing a consumer grade food processor that has a bowl with a diameter of11 cm and a height of 10 cm. The food chopper has a sharp S-shaped bladewith a diameter of 10 cm and rotates at about 1500 rpm when running.

Hydrophilic Silica Blends: Loading Levels of Silica Using Micron SizedSilica EXAMPLES 1-1 TO 1-5

Table 2 and FIG. 5 illustrate the cohesive strength data of formulationscontaining DMDBS and hydrophilic micron sized silica Syloid® 244(Mv=10.8)(micron sized silica range) at a constant total mass of 50 gand various ratios between them. Each formulation is mixed at ambienttemperature for 20 seconds using a consumer grade food processor thathas a bowl with a diameter of 11 cm and a height of 10 cm. TABLE 2Cohesive strength data of hydrophilic powder formulations of DMDBS andSyloid ® 244 (hydrophilic, micron size) Consolidating ConsolidatingDMDBS/ pressure 1 (psf)/ pressure 2 (psf)/ Syloid ® 244 CohesiveCohesive Examples (wt %) strength 1 (psf) strength 2 (psf) Comparative100/0  46/30 86/60 1-1 95/5  43/30 84/59 1-2 90/10 46/31 81/50 1-3 85/1543/28 78/47 1-4 80/20 42/26 80/48 1-5 70/30 42/29 78/48

Comparison may be observed between the cohesive strength of variousDMDBS/silica blends for micron sized silica. It may be seen in Table 2that cohesive strength decreases significantly when more than about 10weight percent of such silica is employed, which is highly desirable.Cohesive strength decrease corresponds to an increase in flowability ofthe additive composition.

Examples 1-2, 1-3, 1-4 and 1-5 show that for micron sized silica, weightratios of between about 10 and about 30 weight percent performparticularly well, having reduced cohesive strength, and thereforeimproved flow properties. Thus, this example illustrates that loadinglevels in the range of about 10-30% are quite useful. A loading level ofbetween about 10 and about 20 percent performed very well, as shown bythe lowermost lines in FIG. 5 (examples 1-3 and 1-4).

Hydrophobic Versus Hydrophilic Silica: Effects when Using Micron SizedSilica EXAMPLES 2-1 AND 2-2

Table 3 and FIG. 6 illustrate the cohesive strength data of formulationscontaining DMDBS and various grades of micron size silica at a constanttotal mass of 50 g and a constant ratio of 97:3 between DMDBS and thecorresponding silica grade. Each formulation is mixed at ambienttemperature for 20 seconds using a consumer grade food processor thathas a bowl with a diameter of 11 cm and a height of 10 cm.

The data generated and displayed in Table 3 shows that for this givensilica loading (3 percent), a hydrophobic silica results in a lowercohesive strength value (better flowability) than hydrophilic silica(compare 26 to 29, and 48 to 54, below). This is seen graphically inFIG. 6, wherein the lowermost line on the graph represents thehydrophobic example, 2-1. TABLE 3 Cohesive strength data of powderformulations of DMDBS and hydrophobic or hydrophilic micron size silicagrades Consolidating Consolidating pressure 1 (psf)/ pressure 2 (psf)/Cohesive Cohesive Examples Micron size silica strength 1 (psf) strength2 (psf) Comparative — 46/30 86/60 2-1 Sipernat ® D13 40/26 75/48(hydrophobic, micron size) 2-2 Sipernat ® 22LS 42/29 80/54 (hydrophilic,micron size)

Hydrophilic Versus Hydrophobic: Effects at Submicron and Micron SizeRanges EXAMPLES 3-1 AND 3-2

Table 4 and FIG. 7 illustrate the cohesive strength data of formulationscontaining DMDBS and various grades of submicron and micron size silicaat a constant total mass of 50 g and a constant ratio of 97:3 betweenDMDBS and the corresponding silica grade. Each formulation is mixed atambient temperature for 20 seconds using a consumer grade food processorthat has a bowl with a diameter of 11 cm and a height of 10 cm. The twoformulations (Examples 2-1 and 2-2) containing DMDBS and micron sizesilica grades are also included here for comparison. TABLE 4 Cohesivestrength data of powder formulations of DMDBS and submicron size ormicron size silica grades Consolidating Consolidating pressure 1 (psf)/pressure 2 (psf)/ Cohesive Cohesive Examples Silica grades strength 1(psf) strength 2 (psf) Comparative — 46/30 86/60 3-1 Aerosil ® R97239/23 78/44 (hydrophobic, submicron size) 3-2 Aerosil ® 300 41/24 74/41(hydrophilic, submicron size) 2-1 Sipernat ® D13 40/26 75/48(hydrophobic, micron size) 2-2 Sipernat ® 22LS 42/29 80/54 (hydrophilic,micron size)

The data above shows that submicron size range silica generallyoutperforms micron size silica. Examples 3-1 and 3-2, as seen in FIG. 7,provide the lowest cohesive strength, and therefore the greatestflowability of the additive composition.

Furthermore, for micron sizes (i.e. 2-1 and 2-2), hydrophobic silica(2-1) outperformed hydrophilic silica (2-2), as shown in the top portionof FIG. 7.

Comparisons of Loading Level for Hydrophobic Submicron Size SilicaParticles EXAMPLES 4-1 TO 4-5

Examples 4-1 to 4-5 (See FIG. 8) are designed for a trial at a largerpilot scale to evaluate the feasibility of the application of theinvention, and to compare loading levels of silica for submicron sizesilica particles in the blend.

Table 5 and FIG. 8 illustrate cohesive strength data of formulationscontaining DMDBS and hydrophobic submicron size silica Aerosil® R972 (afumed hydrophobic, submicron size silica) at a constant total mass of 10kg and five different ratios between them. Each formulation has beenmixed at ambient temperature for 30 seconds using a Lodige Model FKM 130batch mixer equipped with Becker shovels and high speed choppers. TABLE5 Cohesive strength data of powder formulations of DMDBS and Aerosil ®R972 (hydrophobic, submicron size) from pilot scale blenderConsolidating Consolidating DMDBS/ pressure 1 (psf)/ pressure 2 (psf)/Aerosil ® Cohesive Cohesive Examples R972 (wt %) strength 1 (psf)strength 2 (psf) Comparative 100/0  46/30 86/60 4-1 99/1 44/30 82/54 4-298/2 40/25 73/41 4-3 97/3 39/23 74/45 4-4 96/4 38/21 75/49 4-5 95/537/20 72/43

The loading levels employed were between 1% and 5%. Results indicatethat the 5% loading level was superior, and in general, as loadinglevels increased from 1 to 5 percent, the cohesive strength tended todecrease (which correlates to improves results, that is, improved amountof flowability). FIG. 8 shows that the improved results (i.e. lowerline) of greater flowability (lower cohesive strength) is apparent atabout 5% loading for this example of submicron size range silica.

MDBS Based Nucleating Agent EXAMPLES 5-1 AND 5-2

Examples 5-1 to 5-2 employ MDBS bis(p-methylbenzylidene) sorbitol, soldby Milliken & Company as Millad® 3940 brand nucleating agent (which isalso known as “MDBS”). Other sorbitol acetal compounds could be employedequally well in the practice of the invention, and the invention isapplicable for essentially any sorbitol acetal compound.

Table 6 and FIG. 9 illustrate the cohesive strength data of formulationscontaining MDBS and hydrophobic submicron size silica Aerosil® R972 at aconstant total mass of 50 g at two different ratios. Each formulation ismixed at ambient temperature for 20 seconds using a consumer grade foodprocessor that has a bowl with a diameter of 11 cm and a height of 10cm.

The results indicate that 3% silica improved substantially the cohesiveproperties of the MDBS/silica blend, reducing cohesive strength, andthereby improving flowability. TABLE 6 Cohesive strength data of powderformulations of MDBS and Aerosil ® R972 (hydrophobic, submicron size)Consolidating Consolidating pressure 1 (psf)/ pressure 2 (psf)/MDBS/Aerosil ® Cohesive Cohesive Examples R972 (wt %) strength 1 (psf)strength 2 (psf) 5-1 100/0  51/45 92/70 5-2 97/3 46/36 93/66

Haze Measurements EXAMPLES 6-1 AND 6-15

To examine whether the incorporation of silica into DMDBS powder wouldhave negative impact on the haze of polymeric articles made using such ablend, several formulations containing DMDBS and various silica gradesat different ratios were tested for their clarifying function in a gradeof polypropylene random copolymer (as shown in Table 7). The resultsbelow indicate that haze levels for silica samples are less than thecontrol sample which did not use silica (i.e. example 6-1), which showsno undesirable effects upon haze by use of the silica grades indicated.

Standard processing condition comprises the following steps:

a) each polymer composition is composed of polypropylene randomcopolymer flakes (12 MFR) 1000 g, Irganox® 1010 (primary antioxidant,available from Ciba) 0.5 g (500 ppm), Irgafos® 168 (secondaryantioxidant, available from Ciba) 1 g (1000 ppm), calcium stearate (acidscavenger) 0.8 g (800 ppm), DMDBS 2 g (2000 ppm), and silica at variousloadings (see Table 7 for silica's grades and use levels);

b) mixing all components in a high intensity mixer at ambienttemperature for 1 minute;

c) compounding the mixture using a single screw extruder at ca. 230° C.;

d) molding the compounded resin into 2×3×0.05 inch plaques at ca. 230°C. melt temperature; e) at least 12 plaques being collected for hazereading according to ASTM D1003-92 using a haze meter BYK Gardnerhaze-gard plus; and

f) sample plaques are submitted for detection of white specks under anOlympus BX51 upright optical microscope. TABLE 7 Optical performance ofpolypropylene formulations containing 2000 ppm DMDBS versus silica gradeand loading Haze White Examples Silica Loading (ppm) (%) speck (Y/N) 6-1— — 8.5 N 6-2 Aerosil ® 300 60 8.1 N 6-3 (hydrophilic) 100 8.0 N 6-4 2008.1 N 6-5 300 8.1 N 6-6 400 8.1 N 6-7 500 8.1 N 6-8 600 8.2 N 6-9 HDK ®H15 60 8.1 N 6-10 (hydrophobic) 100 7.9 N 6-11 200 8.0 N 6-12 300 8.0 N6-13 400 7.9 N 6-14 500 7.8 N 6-15 600 8.0 NTechnical Conclusions

There are at least three independent key factors that dominate theflowability improvement potential of silica for sorbitol acetalcompounds. The inventions identified herein correspond in some cases tothe discoveries relating to such factors.

Important factors in flowability performance of silica/sorbitol acetalcompound additive compositions are:

1) loading (weight percent) of silica in the additive compositions;

2) hydrophobicity of silica employed; and

3) particle size of silica particles employed in the additivecompositions.

Loading

As shown in Table 2 and FIG. 5, Syloid® 244 does not improve the flowproperties of DMDBS powder additive blends until its dosage is higherthan about 10 wt % of the overall additive composition formulation. Thisis rather unexpected, given that manufacturers of silica in the industryrecommend about 2% silica when silica is employed as a granular orpowder flow aid. Thus, a level of 10% or greater loading is unexpected.

Hydrophobicity

Another important factor in flow improvement is the surface chemicalnature of silica used. As suggested in Table 3 and FIG. 6, hydrophobicsilica (Sipernat® D13) works much better than hydrophilic silica(Sipernat® 22LS)(see Table 1). Together with results from Table 2 andFIG. 5, a conclusion can be made that unusually high loadings of silicamay be lowered to some extent if the right surface chemical nature ofsilica is chosen (hydrophobicity). Sipernat® D13 works at a loading of 3wt % (still higher than conventional loading) comparable to Syloid® 244at a loading of 20 wt %. While not being limited by mechanism, it isbelieved that there may be improved compatibility between the DMDBSparticle surface and the hydrophobic silica particle surface, which maylead to more effective flowability improvement for hydrophobic silicagrades. In general, hydrophobic silica shows improved performance ascompared to hydrophilic silica, especially at submicron loadings.

Particle Size

Another key factor that controls flowability potential for additivecompositions of sorbitol acetal compounds with silica is the particlesize of the silica employed. Table 4 and FIG. 7 demonstrate the flowimproving performance of two different fumed silica grades. Fumed silicais submicron in size, and significantly smaller than micron sizedsilica. Fumed silica performs well in the practice of the invention.

Comparison was made between these two silica grades, which both are inthe submicron size range, but have a different surface chemical nature(Aerosil® R972 is hydrophobic, and Aerosil® 300 is hydrophilic). Theyboth significantly improve the flow properties of DMDBS powder. Theyimprove the flow properties of DMDBS significantly better than micronsize silica grades (Sipernat® D13 and Sipernat® 22LS).

Pilot Scale Trial

To optimize the process and verify the findings, a pilot scale trialusing an industrial blender was performed. The cohesive strength dataconfirmed the findings described above. The formulation of DMDBS withsilica has significantly better flow properties than DMDBS withoutsilica. At the same time, the hydrophobic surface and submicron size ofAerosil® R972 (as one example) renders a much lower effective loadingthan Syloid® 244 (Table 2 and FIG. 5).

It is understood by one of ordinary skill in the art that the presentdiscussion is a description of exemplary embodiments only, and is notintended as limiting the broader aspects of the present invention. Theinvention is shown by example in the appended claims, but is not limitedto such examples.

1. An additive composition comprising: (a) a sorbitol acetal compound,and (b) a silica component, said silica component having a Mv value ofless than about 0.6 μm and a D90 value of less than about 1 μm.
 2. Acomposition according to claim 1 wherein said silica component furtherprovides a Mv value of less than about 0.4 μm and a D90 value of lessthan about 0.6 μm.
 3. A composition according to claim 1 wherein saidsilica component is substantially hydrophobic.
 4. A compositionaccording to claim 1 wherein the weight percentage of the silica in theadditive composition is from about 0.5% to about 30%.
 5. A compositionaccording to claim 1 wherein the weight percentage of the silica in theadditive composition is from about 1% to about 5%.
 6. A polymeric orcopolymeric article of manufacture comprising the additive compositionof claim
 1. 7. An additive composition comprising: (a) a sorbitol acetalcompound, and (b) a silica component, wherein said silica componentcontains a silica fraction, said silica fraction providing at least 1%by weight particles size of less than 1 μm.
 8. A composition accordingto claim 7 wherein the silica component provides a D10 value of lessthan about 0.5 μm.
 9. A composition according to claim 7 wherein saidsilica component is substantially hydrophobic.
 10. A compositionaccording to claim 7 wherein the weight percentage of the silica in theadditive composition is from about 0.5% to about 30%.
 11. A compositionaccording to claim 7 wherein the weight percentage of the silica in theadditive composition is from about 0.5% to about 10%.
 12. A polymeric orcopolymeric article of manufacture comprising the composition of claim7.
 13. An additive composition comprising: (a) a sorbitol acetalcompound, (b) a silica component, said silica component having a Mvvalue of less than about 20 μm and a D90 value of less than about 50 um;(c) wherein the weight percentage of silica in the additive compositionis equal to or greater than about 10%.
 14. A composition according toclaim 13 wherein the silica component further provides a Mv value ofless than about 10 μm, and a D90 value of less than about 25 μm.
 15. Acomposition according to claim 13 wherein the weight percentage ofsilica in the additive composition is from about 10% to about 30%.
 16. Acomposition according to claim 13 wherein said silica is hydrophobic.17. A polymeric or copolymeric article of manufacture comprising thecomposition of claim
 13. 18. An nucleating agent additive compositionthat is substantially free of organic lubricating agents, said additivecomposition consisting essentially of: (a) a sorbitol acetal compound,and (b) a silica component, said silica component having: a Mv of lessthan about 20 μm, and a D90 value of less than 50 μm, and wherein theweight percentage of the silica component in the additive composition isfrom about 1% to about 10%.
 19. A composition according to claim 18wherein said silica component provides a Mv value of less than about 10μm and a D90 value of less than about 25 μm.
 20. A polymeric orcopolymeric article of manufacture comprising the additive compositionof claim
 18. 21. A method of making a nucleated polymeric or copolymericcomposition, said method comprising the steps of: providing a polymer orcopolymer; providing an additive composition, said additive compositioncomprising: asorbitol acetal compound and a silica component, saidsilica component having a Mv value of less than about 0.6 μm and a D90value of less than about 1 μm; feeding and dispersing said additivecomposition into said polymer or copolymer to form a nucleated polymeror copolymer.
 22. A method of making a nucleated polymeric orcopolymeric composition, said method comprising the steps of: providinga polymer or copolymer; providing an additive composition, said additivecomposition having asorbitol acetal compound, said silica componenthaving a Mv value of less than about 20 μm and a D90 value of less thanabout 50 um, and the weight percentage of the silica in the additivecomposition is equal to or greater than about 10%; and dispersing saidadditive composition into said polymer or copolymer to form a nucleatedpolymer or copolymer.
 23. An additive composition comprising: (a) axylitol acetal compound, and (b) a silica component, said silicacomponent having a Mv value of less than about 0.6 μm and a D90 value ofless than about 1 μm.
 24. A composition according to claim 23 whereinsaid silica component further provides a Mv value of less than about 0.4μm and a D90 value of less than about 0.6 μm.
 25. A compositionaccording to claim 23 wherein said silica component is hydrophobic. 26.An additive composition comprising: (a) a xylitol acetal compound, and(b) a silica component, wherein said silica component contains a silicafraction providing at least 1% by weight of said additive composition ofsilica particles, said 1% silica fraction having particles with a sizeof less than 1 μm.